U.S. patent application number 10/391176 was filed with the patent office on 2004-09-23 for p-type materials and mixtures for electronic devices.
This patent application is currently assigned to Eastman Kodak Company. Invention is credited to Klubek, Kevin P., Liao, Liang-Sheng, Tang, Ching W., Vargas, J. Ramon.
Application Number | 20040183066 10/391176 |
Document ID | / |
Family ID | 32824854 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040183066 |
Kind Code |
A1 |
Klubek, Kevin P. ; et
al. |
September 23, 2004 |
P-type materials and mixtures for electronic devices
Abstract
A p-type mixture for use in an electronic device including a
host including a dihydrophenazine compound, and a dopant provided
in the host.
Inventors: |
Klubek, Kevin P.; (Webster,
NY) ; Liao, Liang-Sheng; (Rochester, NY) ;
Vargas, J. Ramon; (Webster, NY) ; Tang, Ching W.;
(Rochester, NY) |
Correspondence
Address: |
Thomas H. Close
Patent Legal Staff
Eastman Kodak Company
343 State Street
Rochester
NY
14650-2201
US
|
Assignee: |
Eastman Kodak Company
|
Family ID: |
32824854 |
Appl. No.: |
10/391176 |
Filed: |
March 18, 2003 |
Current U.S.
Class: |
257/40 ; 313/506;
428/690; 428/917; 544/224; 544/338 |
Current CPC
Class: |
H01L 51/0071 20130101;
H01L 51/0059 20130101; H01L 51/5278 20130101; H01L 51/0058
20130101; H01L 51/0067 20130101; H01L 51/0081 20130101; H01L
51/0051 20130101; H01L 51/0061 20130101; Y10S 428/917 20130101;
H01L 51/006 20130101; H01L 51/5076 20130101; H01L 51/0069
20130101 |
Class at
Publication: |
257/040 ;
428/690; 428/917; 313/506; 544/224; 544/338 |
International
Class: |
H01B 001/12; H05B
033/12 |
Claims
What is claimed is:
1. A p-type mixture for use in an electronic device, comprising: a)
a host including a dihydrophenazine compound; and b) a dopant
provided in the host.
2. A p-type mixture for use in an electronic device, comprising: a)
a host including a dihydrophenazine compound of the formula:
93wherein: R.sub.1 is hydrogen, halogen, alkyl of from 1 to 24
carbon atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.2 to form 5 or 6 member ring
systems; R.sub.4 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.3 to form 5 or 6 member ring
systems; R.sub.5 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl, substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.6 to form 5 or 6 member ring
systems; R.sub.8 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.7 to form 5 or 6 member ring
systems; R.sub.2 and R.sub.3 are individually hydrogen, alkyl of
from 1 to 24 carbon atoms, which are branched, unbranched, or
cyclic, halogen, aryl or substituted aryl of from 5 to 24 carbon
atoms, heterocyclic or substituted heterocyclic, alkenyl or
substituted alkenyl, alkoxy, aryloxy, amino, thioaryl, thioalkyl,
or connected to form 5 or 6 member ring systems; R.sub.6 and
R.sub.7 are individually hydrogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, halogen, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, thioaryl, thioalkyl, or connected to form 5 or 6
member ring systems; R.sub.9 and R.sub.10 are individually
hydrogen, alkyl of from 1 to 24 carbon atoms, which are branched,
unbranched, or cyclic, aryl or substituted aryl of from 5 to 24
carbon atoms, heterocyclic or substituted heterocyclic, alkenyl or
substituted alkenyl; and b) a dopant provided in the host.
3. The p-type mixture according to claim 2 wherein the
dihydrophenazine compound is of the formula: 94
4. The p-type mixture according to claim 2 wherein the
dihydrophenazine compound is of the formula: 95
5. The p-type mixture according to claim 2 wherein the
dihydrophenazine compound is of the formula: 96
6. The p-type mixture according to claim 2 wherein the
dihydrophenazine compound is of the formula: 97
7. The p-type mixture according to claim 2 wherein the
dihydrophenazine compound is of the formula: 98
8. The p-type mixture according to claim 2 wherein the
dihydrophenazine compound is of the formula: 99
9. The p-type mixture according to claim 2 wherein the dopant is of
the formula: 100
10. The p-type mixture according to claim 2 wherein the dopant is
of the formula: 101
11. The p-type mixture according to claim 2 wherein the dopant is
of the formula: 102
12. The p-type mixture according to claim 2 wherein the dopant is:
i) iodine (I.sub.2); ii) iron (III) chloride (FeCl.sub.3); iii)
iron (III) fluoride (FeF.sub.3); or iv) antimony (V) chloride
(SbCl.sub.5).
13. The p-type mixture according to claim 2 wherein the dopant is a
material having strong electron withdrawing properties.
14. A dihydrophenazine for use as a p-type material in an
electronic device.
15. The invention of claim 14 wherein the electronic device is an
OLED device.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Reference is made to commonly assigned U.S. patent
application Ser. No. 10/267,252 filed Oct. 9, 2002 by Liang-Sheng
L. Liao, entitled "Cascaded Organic Electroluminescent Devices With
Improved Voltage Stability", and U.S. patent application Ser. No.
______ filed concurrently herewith by Kevin P. Klubek, entitled
"Cascaded Organic Electroluminescent Devices"; the disclosures of
which are herein incorporated by reference.
FIELD OF INVENTION
[0002] This invention relates to p-type dihydrophenazines and
mixtures for use in electronic devices.
BACKGROUND OF THE INVENTION
[0003] P-type and n-type conductivity refer to the conductivity
characteristics of semiconductor materials. P-type semiconductor
materials are positive charge carriers (hole-transporting) and
n-type semiconductors are negative charge carriers
(electron-transporting). The key element in semiconductor devices
is the p-n junction. A p-n junction is formed when two regions of
opposite conductivity type are adjacent to each other. P-N
junctions have widespread use for many applications such as
semiconductors, power semiconductors, field effect transistors
(FETs), organic light-emitting diodes (OLEDs) and photovoltaic
cells.
[0004] The usefulness of electrically conducting organic materials
may be associated to a large extent with a combination of
properties such as desirable electronic properties (e.g. low
electrical resistivity), chemical stability, and physical and
chemical properties that would permit the preparation of useful
articles for manufacture. The first two properties mentioned above
are shared by a number of inorganic materials well known in the
art, such as metals (e.g. aluminum, silver and copper) or
semiconductors (e.g. gallium and silicon). Devises comprised of
inorganic materials typically are brittle and require demanding
manufacturing processes which make it both difficult and expensive
to fabricate large area displays. However, the wide chemical
versatility of organic molecules gives the organic conductors a
distinct advantage over inorganic materials to the extent that it
is possible to introduce and modify physical and chemical
properties such as solubility, melting point, etc. by relatively
minor changes in the chemical structure of the organic molecules.
In other words, organic conductors or semiconductors open the
possibility for tailor-made electrically conducting materials with
properties not found in inorganic substances. As such, there have
been intensive research efforts in developing organic materials to
be used as conductors or semiconductors for electronic device
applications.
SUMMARY OF THE INVENTION
[0005] It is an object of the present invention to provide organic
p-type materials available for use in electronic devices. It has
been found that dihydrophenazines and mixtures of dihydrophenazines
with dopants are effective as p-type materials.
[0006] This object is obtained by a p-type mixture for use in an
electronic device, comprising:
[0007] a) a host including a dihydrophenazine compound; and
[0008] b) a dopant provided in the host.
[0009] This object is also achieved by a p-type mixture for use in
an electronic device, comprising:
[0010] a) a host including a dihydrophenazine compound of the
formula: 1
[0011] wherein:
[0012] R.sub.1 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.2 to form 5 or 6 member ring
systems;
[0013] R.sub.4 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.3 to form 5 or 6 member ring
systems;
[0014] R.sub.5 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl, substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.6 to form 5 or 6 member ring
systems;
[0015] R.sub.8 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.7 to form 5 or 6 member ring
systems;
[0016] R.sub.2 and R.sub.3 are individually hydrogen, alkyl of from
1 to 24 carbon atoms,
[0017] which are branched, unbranched, or cyclic, halogen, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, thioaryl, thioalkyl, or connected to form 5 or 6
member ring systems;
[0018] R.sub.6 and R.sub.7 are individually hydrogen, alkyl of from
1 to 24 carbon atoms, which are branched, unbranched, or cyclic,
halogen, aryl or substituted aryl of from 5 to 24 carbon atoms,
heterocyclic or substituted heterocyclic, alkenyl or substituted
alkenyl, alkoxy, aryloxy, amino, thioaryl, thioalkyl, or connected
to form 5 or 6 member ring systems;
[0019] R.sub.9 and R.sub.10 are individually hydrogen, alkyl of
from 1 to 24 carbon atoms, which are branched, unbranched, or
cyclic, aryl or substituted aryl of from 5 to 24 carbon atoms,
heterocyclic or substituted heterocyclic, alkenyl or substituted
alkenyl; and
[0020] b) a dopant provided in the host.
ADVANTAGEOUS EFFECT OF THE INVENTION
[0021] The p-type materials described are useful in many different
devices and industries such as in semiconductors and OLEDs. For a
specific application they will be described with reference to OLED
devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 depicts a schematic cross sectional view of a
cascaded OLED in accordance with the present invention, having a
plurality of organic EL units and having a connecting unit in
between each of the organic EL units;
[0023] FIG. 2 depicts a schematic cross sectional view of a
connecting unit having an n-type doped organic layer, an
interfacial layer, and a p-type doped organic layer useful in the
cascaded OLED in accordance with the present invention;
[0024] FIG. 3 is a graph of luminance vs. operational time for
comparative Examples 1 and 2 and for device Examples 3-5 in
accordance with the present invention. All devices were operated at
a constant driving current density of 20 mA/cm.sup.2 and at room
temperature;
[0025] FIG. 4 is a graph of driving voltage vs. operational time
for comparative Examples 1 and 2 and for device Examples 3-5 in
accordance with the present invention. All devices were operated at
a constant driving current density of 20 mA/cm.sup.2 and at room
temperature;
[0026] FIG. 5 is a graph of luminance vs. operational time for
comparative Examples 1 and 2 and for device Examples 6-8 in
accordance with the present invention. All devices were operated at
a constant driving current density of 20 mA/cm.sup.2 and at room
temperature;
[0027] FIG. 6 is a graph of driving voltage vs. operational time
for comparative Examples 1 and 2 and for device Examples 6-8 in
accordance with the present invention. All devices were operated at
a constant driving current density of 20 mA/cm.sup.2 and at room
temperature;
[0028] FIG. 7 is a graph of luminance vs. operational time for
device Examples 7 and 9 in accordance with the present invention.
All devices were operated at a constant driving current density of
20 mA/cm.sup.2 and at room temperature; and
[0029] FIG. 8 is a graph of driving voltage vs. operational time
for device Examples 7 and 9 in accordance with the present
invention. All devices were operated at a constant driving current
density of 20 mA/cm.sup.2 and at room temperature.
[0030] It will be understood that FIGS. 1-2 are not to scale since
the individual layers are too thin and the thickness differences of
various layers too great to permit depiction to scale.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The present invention relates to improved p-type materials.
The following is a description of specific embodiments which use
p-type materials in OLED devices. However, it will be understood
that these materials can be used in other electronic devices, such
as those with p-n junctions, and the present invention is not
limited to OLED devices.
[0032] In commonly assigned U.S. patent application Ser. No.
10/077,270 filed Feb. 15, 2002 by Liang-Sheng L. Liao et al.,
entitled "Providing an Organic Electroluminescent Device Having
Stacked Electroluminescent Units", the disclosure of which is
herein incorporated by reference, the layer structure of a cascaded
OLED (or stacked OLED) has been disclosed. The device structure
comprises an anode, a cathode, a plurality of organic EL units and
a plurality of organic connectors (or connecting units thereafter),
wherein each of the connecting units is disposed between two
organic EL units. The organic EL unit comprises, in sequence, a
hole-transport layer, a light-emitting layer, and an
electron-transport layer, denoted in brief as HTL/LEL/ETL. The
connecting unit comprises, in sequence, an n-type doped organic
layer and a p-type doped organic layer. Thus, in this structure,
the ETL of the EL unit is adjacent to the n-type doped layer of the
connecting unit and the HTL of the EL unit is adjacent to the
p-type doped connecting unit. In this cascaded device structure
only a single external power source is needed to connect to the
anode and the cathode with the positive potential applied to the
anode and the negative potential to the cathode. No other
electrical connections are needed to connect the individual organic
EL units to external electrical power sources.
[0033] For a cascaded OLED to function efficiently, it is necessary
that the optical transparency of the layers constituting the
organic EL units and the connecting units be as high as possible to
allow for radiation generated in the organic EL units to exit the
device. Furthermore, for the radiation to exit through the anode,
the anode should be transparent and the cathode can be opaque,
reflecting, or transparent. For the radiation to exit through the
cathode, the cathode should be transparent and the anode can be
opaque, reflecting or transparent. The layers constituting the
organic EL units are generally optically transparent to the
radiation generated by the EL units, and therefore their
transparency is generally not a concern for the construction of the
cascaded OLEDs. Likewise, the layers constituting the connecting
units can be constructed from selected organic materials and
appropriate n-type or p-type dopants such that their optical
transparency can be made as high as possible. Commonly assigned
U.S. patent application Ser. No. 10/077,270 filed Feb. 15, 2002 by
Liang-Sheng L. Liao et al., entitled "Providing an Organic
Electroluminescent Device Having Stacked Electroluminescent Units",
the disclosure of which is herein incorporated by reference,
discloses the art pertaining to the construction of the cascaded
OLED with the appropriate connecting units.
[0034] Another requirement for the cascaded OLED to function
efficiently is that the connecting unit should provide electron
injection into the electron-transporting layer and the hole
injection into the hole-transporting layer of the two adjacent
organic EL units. The construction of such a connecting unit
capable of providing excellent electron and hole injection has also
been disclosed in commonly assigned U.S. patent application Ser.
No. 10/077,270 filed Feb. 15, 2002 by Liang-Sheng L. Liao et al.,
entitled "Providing an Organic Electroluminescent Device Having
Stacked Electroluminescent Units", the disclosure of which is
herein incorporated by reference. The combination of these device
properties, that is, high optical transparency and excellent charge
injection, offers the cascade OLED high electroluminescence
efficiency and operation at an overall low driving voltage.
[0035] The operational stability of a cascaded OLED is dependent to
a large extent on the stability of the connecting units. In
particular, the driving voltage will be highly dependent on whether
or not the organic connecting unit can provide the necessary
electron and hole injection. It is generally known that the close
proximity of two dissimilar materials may result in diffusion of
matters from one into another, or in interdiffusion of matters
across the boundary between the two. In the case of the cascaded
OLED, if such diffusion were to occur in the connecting unit
between the n-type doped organic layer and the p-type doped organic
layer, the injection properties of this organic connecting unit may
degrade correspondingly due to the fact that the individual n-type
doped layer or p-type doped layer may no longer be sufficiently
electrically conductive. Diffusion or interdiffusion is dependent
on temperature as well as other factors such as electrical field
induced migration. The latter is plausible in cascaded OLED devices
since the operation of OLEDs generally requires an electric field
as high as 10.sup.6 volt per centimeter. To prevent such an
operationally induced diffusion in the connecting units of a
cascaded OLED, an interfacial layer may be introduced in between
the n-type doped layer and the p-type doped layer, which provides a
barrier for interfusion. The construction of connecting units
containing an interfacial layer between the n-type doped layer and
the p-type doped layer has been disclosed in commonly assigned U.S.
patent application Ser. No. 10/267,252 filed Oct. 9, 2002 by
Liang-Sheng L. Liao, entitled "Cascaded Organic Electroluminescent
Devices With Improved Voltage Stability", the disclosures of which
are herein incorporated by reference.
[0036] FIG. 1 shows a cascaded OLED 100 in accordance with the
present invention. This cascaded OLED has an anode 110 and a
cathode 140, at least one of which is transparent. Disposed between
the anode and the cathode are N organic EL units 120, where N is an
integer greater than 1. These organic EL units, cascaded serially
to each other and to the anode and the cathode, are designated
120.1 to 120.N where 120.1 is the 1.sup.st EL unit (adjacent to the
anode) and 120.N is the N.sup.th unit (adjacent to the cathode).
The term, EL unit 120, represents any of the EL units named from
120.1 to 120.N in the present invention. When N is greater than 2,
there are organic EL units not adjacent to the anode or cathode,
and these can be referred to as intermediate organic EL units.
Disposed between any two adjacent organic EL units is a connecting
unit 130. There are a total of N-1 connecting units associated with
N organic EL units and they are designated 130.1 to 130.(N-1).
Connecting unit 130.1 is disposed between organic EL units 120.1
and 120.2, connecting unit 130.2 is disposed between organic EL
units 120.2 and 120.3, and connecting unit 130.(N-1) is disposed
between organic EL units 120.(N-1) and 120.N. The term, connecting
unit 130, represents any of the connecting units named from 130.1
to 130.(N-1) in the present invention. The cascaded OLED 100 is
externally connected to a voltage/current source 150 through
electrical conductors 160.
[0037] Cascaded OLED 100 is operated by applying an electric
potential generated by a voltage/current source 150 between a pair
of contact electrodes, anode 110 and cathode 140, such that anode
110 is at a more positive potential with respect to the cathode
140. This externally applied electrical potential is distributed
among the N organic EL units in proportion to the electrical
resistance of each of these units. The electric potential across
the cascaded OLED causes holes (positively charged carriers) to be
injected from anode 110 into the 1.sup.st organic EL unit 120.1,
and electrons (negatively charged carriers) to be injected from
cathode 140 into the Nth organic EL unit 120.N. Simultaneously,
electrons and holes are generated in, and separated from, each of
the connecting units (130.1-130.(N-1)). Electrons generated in each
of the connecting units (130.1-130.(N-1) are injected towards the
anode. Holes generated in each of the connecting units
(130.1-130.(N-1) are injected towards the cathode. Electrons thus
generated in, for example, connecting unit 130.(N-1) are injected
towards the anode and into the adjacent organic EL unit 120.(N-1).
Likewise, holes generated in the connecting unit 130.(N-1) are
injected towards the cathode and into the adjacent organic EL unit
120.N. Subsequently, these electrons and holes recombine in their
corresponding organic EL units to produce light, which is observed
via the transparent electrode or electrodes of the OLED. In other
words, the electrons injected from cathode are energetically
cascading from the Nth organic EL unit to the 1.sup.st organic EL
unit, and emit light in each of the organic EL units. Therefore, we
use the term "cascaded OLED" in the present invention.
[0038] The same as in commonly assigned U.S. patent application
Ser. No. 10/077,270 filed Feb. 15, 2002 by Liang-Sheng L. Liao et
al., entitled "Providing an Organic Electroluminescent Device
Having Stacked Electroluminescent Units", the disclosure of which
is herein incorporated by reference, each organic EL unit 120 in
the cascaded OLED 100 is capable of supporting hole and
electron-transport, and electron-hole recombination to produce
light. Each organic EL unit 120 can comprise a plurality of layers.
There are many organic EL multilayer structures known in the art
that can be used as the organic EL unit of the present invention.
These include HTL/ETL, HTL/LEL/ETL, HIL/HTL/LEL/ETL,
HIL/HTL/LEL/ETL/EIL, HIL/HTL/electron-blocking layer or
hole-blocking layer/LEL/ETL/EIL, HIL/HTL/LEL/hole-blocking
layer/ETL/EIL. Each organic EL unit in the cascaded OLED can have
the same or different layer structures from other organic EL units.
The layer structure of the 1.sup.st organic EL unit adjacent to the
anode preferably is of HIL/HTL/LEL/ETL, and the layer structure of
the N.sup.th organic EL unit adjacent to the anode preferably is of
HTL/LEL/ETL/EIL, and the layer structure of the intermediate
organic EL units preferably are of HTL/LEL/ETL.
[0039] The organic layers in the organic EL unit 120 can be formed
from small molecule OLED materials or polymeric LED materials, both
known in the art, or combinations thereof. The corresponding
organic layer in each organic EL unit in the cascaded OLED device
can be the same or different from other corresponding organic
layers. Some organic EL units can be polymeric and other units can
be of small molecules.
[0040] Each organic EL unit can be selected in order to optimize
performance or achieve a desired attribute, for example, light
transmission through the OLED multilayer structure, driving
voltage, luminance efficiency, light emission color,
manufacturability, device stability, and so forth.
[0041] In order to minimize driving voltage for the cascaded OLED,
it is desirable to make each organic EL unit as thin as possible
without compromising the electroluminescence efficiency. It is
preferable that each organic EL unit is less than 500 nm thick, and
more preferable that it be 2-200 nm thick. It is also preferable
that each layer within the organic EL unit be 200 nm thick or less,
and more preferable that it be 0.1-100 nm.
[0042] The number of the organic EL units in the cascaded OLED is,
in principle, equal to or more than 2. Preferably, the number of
the organic EL units in the cascaded OLED is such that the
luminance efficiency in units of cd/A is improved or maximized.
[0043] As is known, the conventional OLED comprises an anode, an
organic medium, and a cathode. The cascaded OLED comprises an
anode, a plurality of organic EL units, a plurality of connecting
units, and a cathode.
[0044] The connecting units provided between adjacent organic EL
units are crucial, as they are needed to provide for efficient
electron and hole injection into the adjacent organic EL units. The
layer structure of the connecting unit is shown in FIG. 2. It
comprises, in sequence, an n-type doped organic layer 131, an
optional interfacial layer 132, and a p-type doped organic layer
133. The n-type doped organic layer 131 is adjacent to the ETL of
the organic EL unit towards the anode side, and the p-type doped
organic layer 133 is adjacent to the HTL of the organic EL unit
towards the cathode side. The n-type doped organic layer is chosen
to provide efficient electron injection into the adjacent
electron-transporting layer. The p-type doped organic layer is
chosen to provide efficient hole injection into the adjacent
hole-transporting layer. The use of an optional interfacial layer
in the connecting unit is to prevent possible interdiffusion or
reaction between the n-type doped organic layer and the p-type
doped organic layer. To preserve the operational characteristics of
the cascaded OLED, this additional interfacial layer should not
result in an increase in electrical resistance nor a decrease in
the optical transparency, otherwise the driving voltage would
increase and the light output would decrease. Therefore, the
interfacial layer has at least 90% optical transmission in the
visible region of the spectrum. The chemical composition and the
thickness of the interfacial layer will influence both the
diffusion barrier and optical properties and will therefore need to
be optimized. Because the organic layers are particularly sensitive
to degradation during deposition, the method of deposition will
need to be optimized as well.
[0045] An n-type doped organic layer means that the layer is
electrically conductive, and the charge carriers are primarily
electrons. The conductivity is provided by the formation of a
charge-transfer complex as a result of electron-transfer from the
dopant to the host material. Depending on the concentration and the
effectiveness of the dopant in donating an electron to the host
material, the layer electrical conductivity may range from
semiconducting to conducting. Likewise, a p-type doped organic
layer means that the layer is electrically conductive, and the
charge carriers are primarily holes. The conductivity is provided
by the formation of charge-transfer complex as a result of
hole-transfer from the dopant to the host material. Depending on
the concentration and the effectiveness of the dopant in donating a
hole to the host material, the layer electrical conductivity may
range from semiconducting to conducting.
[0046] The n-type doped organic layer in each connecting unit
comprises a host organic material and at least one n-type dopant.
The host material in the n-type doped organic layer comprises a
small molecule material or a polymeric material, or a combination
thereof. It is preferred that this host material can support
electron-transport. The p-type doped organic layer in each
connecting unit comprises a host organic material and at least one
p-type dopant. The host material comprises a small molecule
material or a polymeric material, or a combination thereof. It is
preferred that this host material can support hole transport. In
general, the host material for the n-type doped layer is different
from the host material for the p-type doped layer because of the
difference in conduction type. But in some instances, some organic
materials can be used as a host in either n-typed or p-type doped
organic layer. These materials are capable of supporting the
transport of either holes or electrons. Upon doping with an
appropriate n-type or p-type dopant, the doped organic layer would
then exhibit primarily either electron-transport or hole-transport,
respectively. The n-type doped concentration or the p-type doped
concentration is preferably in the range of 0.01-20 vol. %. The
total thickness of each connecting unit is typically less than 200
nm, and preferably in the range of about 1 to 150 nm.
[0047] The electron-transporting materials used in conventional
OLED devices represent a useful class of host materials for the
n-type doped organic layer. Preferred materials are metal chelated
oxinoid compounds, including chelates of oxine itself (also
commonly referred to as 8-quinolinol or 8-hydroxyquinoline), such
as tris(8-hydroxyquinoline) aluminum. Other materials include
various butadiene derivatives as disclosed by Tang (U.S. Pat. No.
4,356,429), various heterocyclic optical brighteners as disclosed
by Van Slyke et al. (U.S. Pat. No. 4,539,507), triazines,
hydroxyquinoline derivatives, and benzazole derivatives. Silole
derivatives, such as 2,5-bis(2',2"-bipridin-6-yl)-1,1-dimethyl-3,4-
-diphenyl silacyclopentadiene reported by Murata et al., Applied
Physics Letters, 80, 189, 2002, are also useful host materials.
[0048] The materials used as the n-type dopants in the n-type doped
organic layer of the connecting units include metals or metal
compounds having a work function less than 4.0 eV. Particularly
useful dopants include alkali metals, alkali metal compounds,
alkaline earth metals, and alkaline earth metal compounds. The term
"metal compounds" includes organometallic complexes, metal-organic
salts, and inorganic salts, oxides and halides. Among the class of
metal-containing n-type dopants, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba,
La, Ce, Sm, Eu, Tb, Dy, or Yb, and their inorganic or organic
compounds, are particularly useful. The materials used as the
n-type dopants in the n-type doped organic layer of the connecting
units also include organic reducing agents with strong
electron-donating properties. By "strong electron-donating
properties" it is meant that the organic dopant should be able to
donate at least some electronic charge to the host to form a
charge-transfer complex with the host. Non-limiting examples of
organic molecules include bis(ethylenedithio)-tetrathiafulvalene
(BEDT-TTF), tetrathiafulvalene (TTF), and their derivatives. In the
case of polymeric hosts, the dopant can be any of the above or also
a material molecularly dispersed or copolymerized with the host as
a minor component.
[0049] The hole-transporting materials used in conventional OLED
devices represent a useful class of host materials for the p-type
doped organic layer. Preferred materials include aromatic tertiary
amines having at least one trivalent nitrogen atom that is bonded
only to carbon atoms, at least one of which is a member of an
aromatic ring. In one form the aromatic tertiary amine can be an
arylamine, such as a monoarylamine, diarylamine, triarylamine, or a
polymeric arylamine. Other suitable triarylamines substituted with
one or more vinyl radicals and/or comprising at least one active
hydrogen-containing group are disclosed by Brantley et al. (U.S.
Pat. Nos. 3,567,450 and 3,658,520). A preferred class of aromatic
tertiary amines are those which include at least two aromatic
tertiary amine moieties as described by Van Slyke et al. (U.S. Pat.
Nos. 4,720,432 and 5,061,569). A more preferred class of aromatic
tertiary amines which have been used as p-type host materials are
the starburst amines as described by Xian, Z. et al. (Advanced
Functional Materials (2001), 11(4), 310-314). Non-limiting examples
include N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) and
N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1-biphenyl-4,4'-diamine
(TPD), and N,N,N',N'-tetranaphthyl-benzidine (TNB) and
4,4',4"-tris(N,N-diphenyl- -amino)triphenylamine (TDATA). A
preferred class of tertiary amine and the subject of the present
invention is a compound of the formula: 2
[0050] wherein:
[0051] R.sub.1 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.2 to form 5 or 6 member ring
systems;
[0052] R.sub.4 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.3 to form 5 or 6 member ring
systems;
[0053] R.sub.5 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl, substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.6 to form 5 or 6 member ring
systems;
[0054] R.sub.8 is hydrogen, halogen, alkyl of from 1 to 24 carbon
atoms, which are branched, unbranched, or cyclic, aryl or
substituted aryl of from 5 to 24 carbon atoms, heterocyclic or
substituted heterocyclic, alkenyl or substituted alkenyl, alkoxy,
aryloxy, amino, or connected to R.sub.7 to form 5 or 6 member ring
systems;
[0055] R.sub.2 and R.sub.3 are individually hydrogen, alkyl of from
1 to 24 carbon atoms, which are branched, unbranched, or cyclic,
halogen, aryl or substituted aryl of from 5 to 24 carbon atoms,
heterocyclic or substituted heterocyclic, alkenyl or substituted
alkenyl, alkoxy, aryloxy, amino, thioaryl, thioalkyl, or connected
to form 5 or 6 member ring systems;
[0056] R.sub.6 and R.sub.7 are individually hydrogen, alkyl of from
1 to 24 carbon atoms, which are branched, unbranched, or cyclic,
halogen, aryl or substituted aryl of from 5 to 24 carbon atoms,
heterocyclic or substituted heterocyclic, alkenyl or substituted
alkenyl, alkoxy, aryloxy, amino, thioaryl, thioalkyl, or connected
to form 5 or 6 member ring systems;
[0057] R.sub.9 and R.sub.10 are individually hydrogen, alkyl of
from 1 to 24 carbon atoms, which are branched, unbranched, or
cyclic, aryl or substituted aryl of from 5 to 24 carbon atoms,
heterocyclic or substituted heterocyclic, alkenyl or substituted
alkenyl.
[0058] The materials used as the p-type dopants in the p-type doped
organic layer of the connecting units are oxidizing agents with
strong electron-withdrawing properties. By "strong
electron-withdrawing properties" it is meant that the organic
dopant should be able to accept some electronic charge from the
host to form a charge-transfer complex with the host. Some
non-limiting examples include organic compounds such as
7,7',8,8'-tetracyanoquinodimethane (TCNQ),
2,3,5,6-tetrafluoro-7,7',8,- 8'-tetracyanoquinodimethane
(F.sub.4-TCNQ), 11,11,12,12-tetracyanoquinodim- ethane (TNAP), and
other derivatives of TCNQ, and inorganic oxidizing agents such as
iodine, FeCl.sub.3, FeF.sub.3, SbCl.sub.5, and some other metal
halides. In the case of polymeric hosts, the dopant can be any of
the above or also a material molecularly dispersed or
co-polymerized with the host as a minor component.
[0059] Examples of materials that can be used as host for either
the n-type or p-type doped organic layers include, but are not
limited to: various anthracene derivatives as described in U.S.
Pat. No. 5,972,247; certain carbazole derivatives, such as
4,4-bis(9-dicarbazolyl)-biphenyl (CBP); and distyrylarylene
derivatives such as 4,4'-bis(2,2'-diphenyl vinyl)-1,1'-biphenyl and
as described in U.S. Pat. No. 5,121,029.
[0060] The optional interfacial layer 132 useful in the connecting
unit comprises at least one inorganic semiconducting material or
combinations of more than one of the semiconducting materials.
Suitable semiconducting materials should have an electron energy
band gap less than 4.0 eV. The electron energy band gap is defined
as the energy difference between the highest occupied molecular
orbital and the lowest unoccupied molecular orbital of the
molecule. A useful class of materials can be chosen from the
compounds of elements listed in groups IVA, VA, VIA, VIIA, VIIIA,
IB, IIB, IIIB, IVB, and VB in the Periodic Table of the Elements
(e.g. the Periodic Table of the Elements published by VWR
Scientific Products). These compounds include the carbides,
silicides, nitrides, phosphides, arsenides, oxides, sulfides,
selenides, and tellurides, and mixtures thereof. These
semiconducting compounds can be in either stoichiometric or
non-stoichiometric states, that is they may contain excess or
deficit metal component. Particularly useful materials for the
interfacial layer 132 are the semiconducting oxides of titanium,
zirconium, hafnium, vanadium, niobium, tantalum, chromium,
molybdenum, tungsten, manganese, rhenium, iron, ruthenium, osmium,
cobalt, rhodium, iridium, nickel, palladium, platinum, copper,
zinc, cadmium, gallium, thallium, silicon, germanium, lead, and
antimony, or combinations thereof. Particularly useful materials
for the interfacial layer 132 also including zinc selenide, gallium
nitride, silicon carbide, or combinations thereof.
[0061] The interfacial layer 132 useful in the connecting unit also
can comprise at least one or more metallic materials, at least one
of these metallic materials has a work function higher than 4.0 eV
as listed by Sze, in Physics of Semiconducting Devices, 2.sup.nd
Edition, Wiley, N.Y., 1981, p. 251.
[0062] The thickness of the interfacial layer 132 suitable for the
construction of the connecting units is in the range of 0.05 nm to
10 nm. Preferably, the range is between 0.1 nm to 5 nm for
inorganic semiconducting materials and between 0.05 nm to 1 nmn for
metallic materials.
[0063] The interfacial layer 132 suitable for the construction of
the connecting units is fabricated by thermal evaporation,
electron-beam evaporation, or ion-sputtering deposition. Preferably
the interfacial layer 132 is fabricated by thermal evaporation
which is compatible with the method to deposit organic layers.
[0064] The cascaded OLED is typically provided over a supporting
substrate where either the cathode or anode can be in contact with
the substrate. The electrode in contact with the substrate is
conveniently referred to as the bottom electrode. Conventionally,
the bottom electrode is the anode, but the present invention is not
limited to that configuration. The substrate can either be light
transmissive or opaque, depending on the intended direction of
light emission. The light transmissive property is desirable for
viewing the EL emission through the substrate. Transparent glass or
plastic is commonly employed in such cases. For applications where
the EL emission is viewed through the top electrode, the
transmissive characteristic of the bottom support is immaterial,
and therefore can be light transmissive, light absorbing or light
reflective. Substrates for use in this case include, but are not
limited to, glass, plastic, semiconductor materials, silicon,
ceramics, and circuit board materials. Of course, it is necessary
to provide in these device configurations a light-transparent top
electrode.
[0065] When EL emission is viewed through anode 110, the anode
should be transparent or substantially transparent to the emission
of interest. Common transparent anode materials used in the present
invention are indium-tin oxide (ITO), indium-zinc oxide (IZO) and
tin oxide, but other metal oxides can work including, but not
limited to, aluminum- or indium-doped zinc oxide, magnesium-indium
oxide, and nickel-tungsten oxide. In addition to these oxides,
metal nitrides, such as gallium nitride, and metal selenides, such
as zinc selenide, and metal sulfides, such as zinc sulfide, can be
used as the anode. For applications where EL emission is viewed
only through the cathode electrode, the transmissive
characteristics of the anode are immaterial and any conductive
material can be used, transparent, opaque or reflective. Example
conductors for this application include, but are not limited to,
gold, iridium, molybdenum, palladium, and platinum. Typical anode
materials, transmissive or otherwise, have a work function higher
than 4.0 eV. Desired anode materials are commonly deposited by any
suitable means such as evaporation, sputtering, chemical vapor
deposition, or electrochemical means. Anodes can be patterned using
well known photolithographic processes. Optionally, anodes may be
polished prior to application of other layers to reduce surface
roughness so as to minimize electrical shorts or enhance
reflectivity.
[0066] While not always necessary, it is often useful to provide a
HIL in the 1.sup.st organic EL unit to contact the anode 110. The
HIL can serve to improve the film formation property of subsequent
organic layers and to facilitate injection of holes into the HTL
reducing the driving voltage of the cascaded OLED. Suitable
materials for use in the HIL include, but are not limited to,
porphyrinic compounds as described in U.S. Pat. No. 4,720,432,
plasma-deposited fluorocarbon polymers as described in U.S. Pat.
No. 6,208,075, and some aromatic amines, for example, the starburst
amine, TDATA (4,4',4"-tris[N,N-diphenyl-amino) triphenylamine).
Alternative hole-injecting materials reportedly useful in organic
EL devices are described in EP 0 891 121 A1 and EP 1 029 909
A1.
[0067] The HTL in organic EL units contains at least one
hole-transporting compound such as an aromatic tertiary amine,
where the latter is understood to be a compound containing at least
one trivalent nitrogen atom that is bonded only to carbon atoms, at
least one of which is a member of an aromatic ring. In one form the
aromatic tertiary amine can be an arylamine, such as a
monoarylamine, diarylamine, triarylamine, or a polymeric arylamine.
Exemplary monomeric triarylamines are illustrated by Klupfel et al.
U.S. Pat. No. 3,180,730. Other suitable triarylamines substituted
with one or more vinyl radicals and/or comprising at least one
active hydrogen containing group are disclosed by Brantley et al.
U.S. Pat. Nos. 3,567,450 and 3,658,520.
[0068] A more preferred class of aromatic tertiary amines are those
which include at least two aromatic tertiary amine moieties as
described in U.S. Pat. Nos. 4,720,432 and 5,061,569. The HTL can be
formed of a single or a mixture of aromatic tertiary amine
compounds. Illustrative of useful aromatic tertiary amines are the
following:
[0069] 1,1-Bis(4-di-p-tolylaminophenyl)cyclohexane
[0070] 1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane
[0071] 4,4'-Bis(diphenylamino)quadriphenyl
[0072] Bis(4-dimethylamino-2-methylphenyl)-phenylmethane
[0073] N,N,N-Tri(p-tolyl)amine
[0074]
4-(di-p-tolylamino)-4'-[4(di-p-tolylamino)-styryl]stilbene
[0075] N,N,N',N'-Tetra-p-tolyl-4-4'-diaminobiphenyl
[0076] N,N,N',N'-Tetraphenyl-4,4'-diaminobiphenyl
[0077] N,N,N',N'-tetra-1-naphthyl-4,4'-diaminobiphenyl
[0078] N,N,N',N'-tetra-2-naphthyl-4,4'-diaminobiphenyl
[0079] N-Phenylcarbazole
[0080] 4,4'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl
[0081] 4,4'-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl
[0082] 4,4"-Bis[N-(1-naphthyl)-N-phenylamino].sub.p-terphenyl
[0083] 4,4'-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl
[0084] 4,4'-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl
[0085] 1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene
[0086] 4,4'-Bis[N-(9-anthryl)-N-phenylamino]biphenyl
[0087] 4,4"-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl
[0088] 4,4'-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl
[0089] 4,4'-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl
[0090] 4,4'-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl
[0091] 4,4'-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl
[0092] 4,4'-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl
[0093] 4,4'-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl
[0094] 2,6-Bis(di-p-tolylamino)naphthalene
[0095] 2,6-Bis[di-(1-naphthyl)amino]naphthalene
[0096] 2,6-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene
[0097] N,N,N',N'-Tetra(2-naphthyl)-4,4"-diamino-p-terphenyl
[0098] 4,4'-Bis
{N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl
[0099] 4,4'-Bis[N-phenyl-N-(2-pyrenyl)amino]biphenyl
[0100] 2,6-Bis[N,N-di(2-naphthyl)amine]fluorene
[0101] 1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene
[0102] 4,4',4"-tris[(3-methylphenyl)phenylamino]triphenylamine
[0103] Another class of useful hole-transporting materials includes
polycyclic aromatic compounds as described in EP 1 009 041.
Tertiary aromatic amines with more than two amine groups may be
used including oligomeric materials. In addition, polymeric
hole-transporting materials can be used such as
poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole,
polyaniline, and copolymers such as poly(3,4-ethylenedioxyth-
iophene)/poly(4-styrenesulfonate) also called PEDOT/PSS.
[0104] As more fully described in U.S. Pat. Nos. 4,769,292 and
5,935,721, the LEL in organic EL units includes a luminescent or
fluorescent material where electroluminescence is produced as a
result of electron-hole pair recombination in this region. The LEL
can be comprised of a single material, but more commonly consists
of a host material doped with a guest compound or compounds where
light emission comes primarily from the dopant and can be of any
color. The host materials in the LEL can be an
electron-transporting material, as defined below, a
hole-transporting material, as defined above, or another material
or combination of materials that support hole-electron
recombination. The dopant is usually chosen from highly fluorescent
dyes, but phosphorescent compounds, e.g., transition metal
complexes as described in WO 98/55561, WO 00/18851, WO 00/57676,
and WO 00/70655 are also useful. Dopants are typically coated as
0.01 to 10% by weight into the host material. Polymeric materials
such as polyfluorenes and polyvinylarylenes (e.g.,
poly[p-phenylenevinylene], PPV) can also be used as the host
material. In this case, small molecule dopants can be molecularly
dispersed into the polymeric host, or the dopant could be added by
copolymerizing a minor constituent into the host polymer.
[0105] An important relationship for choosing a dye as a dopant is
a comparison of the electron energy band gap. For efficient energy
transfer from the host to the dopant molecule, a necessary
condition is that the band gap of the dopant is smaller than that
of the host material. For phosphorescent emitters it is also
important that the host triplet energy level of the host be high
enough to enable energy transfer from host to dopant.
[0106] Host and emitting molecules known to be of use include, but
are not limited to, those disclosed in U.S. Pat. Nos. 4,768,292;
5,141,671; 5,150,006; 5,151,629; 5,405,709; 5,484,922; 5,593,788;
5,645,948; 5,683,823; 5,755,999; 5,928,802; 5,935,720; 5,935,721;
and 6,020,078.
[0107] Metal complexes of 8-hydroxyquinoline (oxine) and similar
derivatives constitute one class of useful host compounds capable
of supporting electroluminescence. Illustrative of useful chelated
oxinoid compounds are the following:
[0108] CO-1: Aluminum trisoxine [alias,
tris(8-quinolinolato)aluminum(III)- ]
[0109] CO-2: Magnesium bisoxine [alias,
bis(8-quinolinolato)magnesium(II)]
[0110] CO-3: Bis[benzo{f}-8-quinolinolato]zinc (II)
[0111] CO-4:
Bis(2-methyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis(2-met-
hyl-8-quinolinolato) aluminum(III)
[0112] CO-5: Indium trisoxine [alias,
tris(8-quinolinolato)indium]
[0113] CO-6: Aluminum tris(5-methyloxine) [alias,
tris(5-methyl-8-quinolin- olato) aluminum(III)]
[0114] CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)]
[0115] CO-8: Gallium oxine [alias,
tris(8-quinolinolato)gallium(III)]
[0116] CO-9: Zirconium oxine [alias,
tetra(8-quinolinolato)zirconium(IV)]
[0117] Other classes of useful host materials include, but are not
limited to, derivatives of anthracene, such as
9,10-di-(2-naphthyl)anthracene and derivatives thereof as described
in U.S. Pat. No. 5,935,721, distyrylarylene derivatives as
described in U.S. Pat. No. 5,121,029, and benzazole derivatives,
for example, 2,2', 2"-(1,3,5-phenylene)tris[1-phen-
yl-1H-benzimidazole]. Carbazole derivatives are particularly useful
hosts for phosphorescent emitters.
[0118] Useful fluorescent dopants include, but are not limited to,
derivatives of anthracene, tetracene, xanthene, perylene, rubrene,
coumarin, rhodamine, and quinacridone, dicyanomethylenepyran
compounds, thiopyran compounds, polymethine compounds, pyrilium and
thiapyrilium compounds, fluorene derivatives, periflanthene
derivatives, indenoperylene derivatives, bis(azinyl)amine boron
compounds, bis(azinyl)methane compounds, and carbostyryl
compounds.
[0119] Preferred thin film-forming materials for use in forming the
ETL in the organic EL units of the present invention are metal
chelated oxinoid compounds, including chelates of oxine itself
(also commonly referred to as 8-quinolinol or 8-hydroxyquinoline).
Such compounds help to inject and transport electrons, exhibit high
levels of performance, and are readily fabricated in the form of
thin films. Exemplary oxinoid compounds were listed previously.
[0120] Other electron-transporting materials include various
butadiene derivatives as disclosed in U.S. Pat. No. 4,356,429 and
various heterocyclic optical brighteners as described in U.S. Pat.
No. 4,539,507. Benzazoles and triazines are also useful
electron-transporting materials.
[0121] While not always necessary, it is often useful to provide an
electron injection layer (EIL) in the N.sup.th organic EL unit to
contact the cathode 140. The EIL can serve to facilitate injection
of electrons into the ETL and to increase the electrical
conductivity resulting in a low driving voltage of the cascaded
OLED. Suitable materials for use in the EIL are the aforementioned
ETL with strong reducing agents as dopants or with low work
function metals (<4.0 eV) as dopants described in aforementioned
n-type doped organic layer for use in the connecting units.
Alternative inorganic electron-injecting materials can also be
useful in the organic EL unit which will be described in following
paragraph.
[0122] When light emission is viewed solely through the anode, the
cathode 140 used in the present invention can be comprised of
nearly any conductive material. Desirable materials have good
film-forming properties to ensure good contact with the underlying
organic layer, promote electron injection at low voltage, and have
good stability. Useful cathode materials often contain a low work
function metal (<4.0 eV) or metal alloy. One preferred cathode
material is comprised of a Mg:Ag alloy wherein the percentage of
silver is in the range of 1 to 20%, as described in U.S. Pat. No.
4,885,221. Another suitable class of cathode materials includes
bilayers comprising a thin inorganic EIL in contact with organic
layer (e.g., ETL), which is capped with a thicker layer of a
conductive metal. Here, the inorganic EIL preferably includes a low
work function metal or metal salt, and if so, the thicker capping
layer does not need to have a low work function. One such cathode
is comprised of a thin layer of LiF followed by a thicker layer of
Al as described in U.S. Pat. No. 5,677,572. Other useful cathode
material sets include, but are not limited to, those disclosed in
U.S. Pat. Nos. 5,059,861; 5,059,862; and 6,140,763.
[0123] When light emission is viewed through the cathode, the
cathode must be transparent or nearly transparent. For such
applications, metals must be thin or one must use transparent
conductive oxides, or a combination of these materials. Optically
transparent cathodes have been described in more detail in U.S.
Pat. Nos. 4,885,211; 5,247,190; 5,703,436; 5,608,287; 5,837,391;
5,677,572; 5,776,622; 5,776,623; 5,714,838; 5,969,474; 5,739,545;
5,981,306; 6,137,223; 6,140,763; 6,172,459; 6,278,236; 6,284,393;
JP 3,234,963; and EP 1 076 368. Cathode materials are typically
deposited by thermal evaporation, electron-beam evaporation,
ion-sputtering, or chemical vapor deposition. When needed,
patterning can be achieved through many well known methods
including, but not limited to, through-mask deposition, integral
shadow masking, for example, as described in U.S. Pat. No.
5,276,380 and EP 0 732 868, laser ablation, and selective chemical
vapor deposition.
[0124] In some instances, LEL and ETL in the organic EL units can
optionally be collapsed into a single layer that serves the
function of supporting both light emission and
electron-transportation. It is also known in the art that emitting
dopants may be added to the HTL, which may serve as a host.
Multiple dopants may be added to one or more layers in order to
create a white-emitting OLED, for example, by combining blue- and
yellow-emitting materials, cyan- and red-emitting materials, or
red-, green-, and blue-emitting materials. White-emitting devices
are described, for example, in U.S. patent application Publication
2002/0025419 A1; U.S. Pat. Nos. 5,683,823; 5,503,910; 5,405,709;
5,283,182; EP 1 187 235; and EP 1 182 244.
[0125] Additional layers such as electron or hole-blocking layers
as taught in the art may be employed in devices of the present
invention. Hole-blocking layers are commonly used to improve
efficiency of phosphorescent emitter devices, for example, as in
U.S. Patent Application Publication 2002/0015859 A1.
[0126] The organic materials mentioned above are suitably deposited
through a vapor-phase method such as thermal evaporation, but can
be deposited from a fluid, for example, from a solvent with an
optional binder to improve film formation. If the material is a
polymer, solvent deposition is useful but other methods can be
used, such as sputtering or thermal transfer from a donor sheet.
The material to be deposited by thermal evaporation can be
vaporized from an evaporation "boat" often comprised of a tantalum
material, e.g., as described in U.S. Pat. No. 6,237,529, or can be
first coated onto a donor sheet and then sublimed in closer
proximity to the substrate. Layers with a mixture of materials can
utilize separate evaporation boats or the materials can be
pre-mixed and coated from a single boat or donor sheet. Patterned
deposition can be achieved using shadow masks, integral shadow
masks (U.S. Pat. No. 5,294,870), spatially-defined thermal dye
transfer from a donor sheet (U.S. Pat. Nos. 5,688,551; 5,851,709;
and 6,066,357) an inkjet method (U.S. Pat. No. 6,066,357).
[0127] Most OLED devices are sensitive to moisture or oxygen, or
both, so they are commonly sealed in an inert atmosphere such as
nitrogen or argon, along with a desiccant such as alumina, bauxite,
calcium sulfate, clays, silica gel, zeolites, alkaline metal
oxides, alkaline earth metal oxides, sulfates, or metal halides and
perchlorates. Methods for encapsulation and desiccation include,
but are not limited to, those described in U.S. Pat. No. 6,226,890.
In addition, barrier layers such as SiOx, Teflon, and alternating
inorganic/polymeric layers are known in the art for
encapsulation.
[0128] OLED devices of the present invention can employ various
well known optical effects in order to enhance its properties if
desired. This includes optimizing layer thicknesses to yield
maximum light transmission, providing dielectric mirror structures,
replacing reflective electrodes with light-absorbing electrodes,
providing anti-glare or anti-reflection coatings over the display,
providing a polarizing medium over the display, or providing
colored, neutral density, or color conversion filters over the
display. Filters, polarizers, and anti-glare or anti-reflection
coatings may be specifically provided over the cover or as part of
the cover.
[0129] The entire contents of the patents and other publications
referred to in this specification are incorporated herein by
reference.
Synthesis of Invented P-Type Host Materials
[0130] Dihydrophenazine derivatives can be synthesized in two
steps. Step one involves a condensation reaction between an aryl
dihydroxy derivative and an aryl diamino derivative to produce a
dihydrophenzine intermediate. These intermediates, which are prone
to oxidation if proper precaution is not taken, are then
N-alkylated or N-arylated using well known Pd catalyzed cross
coupling chemistry. Table 1 lists many different compounds [V-LXV]
that can be made using the general synthesis.
[0131] The synthesis of compounds I-IV is illustrated in the
synthetic scheme. Compounds I-IV are then reacted with the
appropriate aryl bromide to yield compounds V-XVII.
[0132] Synthesis of 5,10-dihydrophenazine (I)
[0133] Synthesized according to Mikulla, Markus; Mulhaupt, Rolf,
Macromol. Chem. Phys., 199, 795-805, (1998).
[0134] Synthesis of 5,12-dihydro-benzo[b]phenazine (II)
[0135] 2,3-dihydroxynapthalene (10 g, 62.5 mmol),
1,2-phenylenediamine (6.75 g, 62.5 mmol) and N,N-dimethylaniline
(54 ml) are placed into a round bottom flask under nitrogen
atmosphere. Mixture is stirred at reflux. Reaction is monitored by
TLC (CH.sub.2Cl.sub.2:Heptane/1:1) until all
2,3-dihydroxynaphthalene has reacted (.about.3 hours). After
cooling to room temperature, toluene (100 ml) is added and solid is
collected by vacuum filtration. After washing with toluene (50 ml),
ethanol (100 ml) and hexanes (50 ml), the product is dried under
vacuum to yield 11.0 g (76% yield) of light yellow solid.
[0136] Synthesis of 5,12-dihydro-2,3-dimethyl-benzo[b]phenazine
(III)
[0137] 2,3-dihydroxynapthalene (10 g, 62.5 mmol),
4,5-dimethyl-1,2-phenyle- nediamine (8.5 g, 62.5 mmol) and
N,N-dimethylaniline (54 ml) are placed into a round bottom flask
under nitrogen atmosphere. Mixture is stirred at reflux. Reaction
is monitored by TLC (CH.sub.2Cl.sub.2:Heptane/1:1) until all
2,3-dihydroxynaphthalene has reacted (.about.3 hours). After
cooling to room temperature, toluene (100 ml) is added and solid is
collected by vacuum filtration. After washing with toluene (50 ml),
ethanol (100 ml) and hexanes (50 ml), the product is dried under
vacuum to yield 23.3 g (33% yield) of light yellow solid.
[0138] Synthesis of 6,13-dihydro-dibenzo[b]phenazine (IV)
[0139] 2,3-dihydroxynapthalene (10 g, 62.5 mmol),
2,3-diaminonaphthalene (9.9 g, 62.5 mmol) and N,N-dimethylaniline
(54 ml) are placed into a round bottom flask under nitrogen
atmosphere. Mixture is stirred at reflux. Reaction is monitored by
TLC (CH.sub.2Cl.sub.2:Heptane/1:1) until all
2,3-dihydroxynaphthalene has reacted (.about.3 hours). After
cooling to room temperature, toluene (100 ml) is added and solid is
collected by vacuum filtration. After washing with toluene (50 ml),
ethanol (100 ml) and hexanes (50 ml), the product is dried under
vacuum to yield 11.5 g (65% yield) of light yellow solid.
Procedure for the Pd Catalyzed Cross Coupling Reaction of
Dihydrophenazines (I-IV) with Aryl Bromides
[0140] Dihdyrophenazine derivative, (1 equivalent), aryl bromide
(2.2 equivalents), sodium tert-butoxide (3.0 equivalents),
[Pd.sub.2(dba).sub.3] tris(dibenzylideneacetone)dipalladium(0) (3
mol % of dihydrophenazine derivative), tri-tert-butylphosphine (0.8
equivalents of Pd catalyst), and sodium tert-butoxide (3
equivalents) were all placed into a round bottom flask under a
nitrogen atmosphere. Anhydrous toluene is added using a cannula and
mixture is heated at reflux overnight. Two workup procedures were
used depending on the solubility of the product in toluene.
[0141] Workup Procedure 1 (product not soluble in toluene): Upon
cooling the reaction to room temperature, the precipitated solid is
collected by vacuum filtration and washed with additional toluene.
The filter cake is then washed extensively with water, followed by
ethanol, cold tetrahydrofuran and lastly, hexanes. The product is
then dried in an oven to give pure material.
[0142] Workup Procedure 2 (product is soluble in toluene): Reaction
mixture is filtered while hot and the filter is washed with
additional toluene. The filtrate is concentrated to a dark solid.
After dissolving in CH.sub.2Cl.sub.2 and passing through a pad of
silica gel, solvent is removed by rotary evaporation. Hexane is
added and product is collected by filtration and dried in an oven
to give pure material.
[0143] After products are collected by filtration and dried
thoroughly, all materials are sublimed by train sublimation at 600
m Torr.
[0144] Synthesis of Specific Compounds
Synthesis Example 1 (Compound VI)
[0145] The above general procedure was followed using compound (II)
[3.0 g, 12.9 mmol], 4-bromotoluene [4.86 g, 28.5 mmol], sodium
tert-butoxide [3.2 g, 33.3 mmol], Pd.sub.2(dba).sub.3 [300 mg, 0.32
mmol], few drops tri-tert-butylphosphine and 50 ml toluene. Workup
procedure 2 was used which gave 3.1 g (58% yield) of (VI) as a
brown solid after sublimation. FD-MS (m/z): 412.
Synthesis Example 2 (Compound VIII)
[0146] The above general procedure was followed using compound (II)
[3.0 g, 12.9 mmol], 4-bromobiphenyl [6.63 g, 28.4 mmol],], sodium
tert-butoxide [3.2 g, 33.3 mmol], Pd.sub.2(dba).sub.3 [300 mg, 0.32
mmol], few drops tri-tert-butylphosphine and 50 ml toluene. Workup
procedure 2 was used which gave 5.1 g (74% yield) of (VIII) as an
orange solid after sublimation. FD-MS (m/z): 536.
Synthesis Example 3 (Compound X)
[0147] The above general procedure was followed using compound
(III) [3.0 g, 11.5 mmol], 2-bromonaphthalene [4.95 g, 23.0 mmol],
sodium tert-butoxide [3.4 g, 35.4 mmol), Pd.sub.2(dba).sub.3 [300
mg, 0.32 mmol], few drops tri-tert-butylphosphine and 50 ml
toluene. Workup procedure 1 was used which gave 4.0 g (68% yield)
of (X) as a yellow solid after sublimation. FD-MS (m/z): 512.
Synthesis Example 4 (Compound XIII)
[0148] The above general procedure was followed using compound (IV)
[3.0 g, 10.6 mmol], 4-bromotoluene [4.0 g, 23.4 mmol], sodium
tert-butoxide [3.2 g, 33.3 mmol], Pd.sub.2(dba).sub.3 [300 mg, 0.32
mmol], few drops tri-tert-butylphosphine and 50 ml toluene. Workup
procedure 1 was used which gave 3.2 g (65% yield) of (XIII) as a
yellow solid after sublimation. FD-MS (m/z):
[0149] 462.
Synthesis Example 5 (Compound XIV)
[0150] The above general procedure was followed using compound (IV)
[2.6 g, 9.2 mmol], 2-bromonaphthalene [4.0 g, 19.3 mmol], sodium
tert-butoxide [3.0 g, 31.2 mmol],], Pd.sub.2(dba).sub.3 [300 mg,
0.32 mmol], few drops tri-tert-butylphosphine and 50 ml toluene.
Workup procedure 1 was used which gave 4.2 g (85% yield) of (XIV)
as an orange solid after sublimation. FD-MS (m/z):
[0151] 534.
Synthesis Example 6 (Compound XV)
[0152] The above general procedure was followed using compound (IV)
[3.0 g, 10.6 mmol], 2-bromo-6-methoxynaphthalene [5.55 g, 23.4
mmol], sodium tert-butoxide [3.2 g, 33.3 mmol], Pd.sub.2(dba).sub.3
[300 mg, 0.32 mmol], few drops tri-tert-butylphosphine and 50 ml
toluene. Workup procedure 1 was used which gave 4.0 g (63% yield)
of (XV) as a yellow solid after sublimation. FD-MS (m/z): 594.
Synthesis Example 7 (Compound XVII)
[0153] The above general procedure was followed using compound
(III) [3.0 g, 11.5 mmol],
4-bromo-N,N-bis(4-methylphenyl)-benzenamine [8.5 g, 24 mmol],],
sodium tert-butoxide [3.4 g, 35.4 mmol), Pd.sub.2(dba).sub.3 [300
mg, 0.32 mmol], few drops tri-tert-butylphosphine and 50 ml
toluene. Workup procedure 1 was used which gave 5.0 g (54% yield)
of (XVII) as a yellow solid after sublimation. FD-MS (m/z): 802.
34
1TABLE 1 P-Type Host Materials: Compound: 5 (V) 6 (VI) 7 (VII) 8
(VIII) 9 (IX) 10 (X) 11 (XI) 12 (XII) 13 (XIII) 14 (XIV) 15 (XV) 16
(XVI) 17 (XVII) 18 (XVIII) 19 (XIX) 20 (XX) 21 (XXI) 22 (XXII) 23
(XXIII) 24 (XXIV) 25 (XXV) 26 (XXVI) 27 (XXVII) 28 (XXVIII) 29
(XXIX) 30 (XXX) 31 (XXXI) 32 (XXXII) 33 (XXXIII) 34 (XXXIV) 35
(XXXV) 36 (XXXVI) 37 (XXXVII) 38 (XXXVIII) 39 (XXXIX) 40 (XL) 41
(XLI) 42 (XLII) 43 (XLIII) 44 (XLIV) 45 (XLV) 46 (XLVI) 47 (XLVII)
48 (XLVIII) 49 (XLIX) 50 (L) 51 (LI) 52 (LII) 53 (LIII) 54 (LIV) 55
(LV) 56 (LVI) 57 (LVII) 58 (LVIII) 59 (LIX) 60 (LX) 61 (LXI) 62
(LXII) 63 (LXIII) 64 (LXIV) 65 (LXV) 66 (LXVI) 67 (LXVII) 68
(LXVIII) 69 (LXIX) 70 (LXX) 71 (LXXI) 72 (LXXII) 73 (LXXIII) 74
(LXXIV) 75 (LXXV) 76 (LXXVI) 77 (LXXVII) 78 (LXXVIII) 79 (LXXIX) 80
(LXXX) 81 (LXXXI) 82 (LXXXII) 83 (LXXXIII) 84 (LXXXIV) 85 (LXXXV)
86 (LXXXVI) 87 (LXXXVII) 88 (LXXXVIII) 89 (LXXXIX) 90 (XC) 91 (XCI)
92 (XCII)
Device Examples
[0154] The following device examples are presented for a further
understanding of the present invention. For purposes of brevity,
the materials and layers formed therefrom will be abbreviated as
given below.
2 ITO: indium-tin-oxide; used in forming the transparent anode on
glass substrates CFx: polymerized fluorocarbon layer; used in
forming a hole-injecting layer on top of ITO NPB:
N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine; used in forming
the hole-transporting layer in the organic EL unit, and also used
as the host in forming the p-type doped organic layer in the
connecting unit Alq: tris(8-hydroxyquinoline)aluminum(III); used in
forming both the electron-transporting layer in the organic EL
unit, and also used as host in forming the n-type doped organic
layer in the connecting unit F.sub.4-
2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquinodimethane; used as
TCNQ: p-type dopant in forming the p-type doped organic layer in
the connecting unit Li: Lithium; used as n-type dopant in forming
the n-type doped organic layer in the connecting unit Mg:Ag:
magnesium:silver at a ratio of 10:0.5 by volume; used in forming
the cathode.
[0155] The electroluminescence characteristics of all the
fabricated devices were evaluated using a constant current source
and a photometer at room temperature. The fabricated devices are
operated at 20 mA/cm.sup.2 and at the room temperature for
operational stability test.
Example 1 (Conventional OLED--Comparative)
[0156] The preparation of a conventional non-cascaded OLED is as
follows. A .about.1.1 mm thick glass substrate coated with a
transparent ITO conductive layer was cleaned and dried using a
commercial glass scrubber tool. The thickness of ITO is about 42 nm
and the sheet resistance of the ITO is about 68 .OMEGA./square. The
ITO surface was subsequently treated with oxidative plasma to
condition the surface as an anode. A layer of CFx, 1 nm thick, was
deposited on the clean ITO surface as the HIL by decomposing
CHF.sub.3 gas in RF plasma treatment chamber. The substrate was
then transferred into a vacuum deposition chamber for deposition of
all other layers on top of the substrate. The following layers were
deposited in the following sequence by sublimation from a heated
boat under a vacuum of approximately 10.sup.-6 Torr:
[0157] (1) a HTL, 75 nm thick, consisting of NPB;
[0158] (2) an ETL (also serving as the emissive layer), 60 nm
thick, consisting of Alq;
[0159] (3) a cathode, approximately 210 nm thick, consisting of
Mg:Ag.
[0160] After the deposition of these layers, the device was
transferred from the deposition chamber into a dry box for
encapsulation. The completed device structure is denoted as
ITO/CFx/NPB(75)/Alq(60)/Mg:Ag.
[0161] This device requires a driving voltage of 7.3 V to pass 20
mA/cm.sup.2. Its luminance is 495 cd/m.sup.2 and its luminance
efficiency is about 2.5 cd/A. The luminance decay vs. operational
time is shown in both FIGS. 3 and 5, and the voltage evolution vs.
operational time is shown in both FIGS. 4 and 6. After 300 hours'
operation, the luminance is dropped by about 20%, but the driving
voltage is basically unchanged.
Example 2 (Comparative)
[0162] The preparation of a cascaded OLED is as follows. A 1.1 mm
thick glass substrate coated with a transparent ITO conductive
layer was cleaned and dried using a commercial glass scrubber tool.
The thickness of ITO is about 42 nm and the sheet resistance of the
ITO is about 68 .OMEGA./square. The ITO surface was subsequently
treated with oxidative plasma to condition the surface as an anode.
A layer of CFx, 1 nm thick, was deposited on the clean ITO surface
as the HIL by decomposing CHF.sub.3 gas in RF plasma treatment
chamber. The substrate was then transferred into a vacuum
deposition chamber for deposition of all other layers on top of the
substrate. The following layers were deposited in the following
sequence by sublimation from a heated boat under a vacuum of
approximately 10.sup.-6 Torr:
[0163] (1) a HTL, 90 nm thick, consisting of NPB;
[0164] (2) an ETL (also serving as the emissive layer), 30 nm
thick, consisting of Alq;
[0165] [NPB(90 nm)/Alq(30 nm), denoted as EL1, consists of the
1.sup.st EL unit];
[0166] (3) a n-type doped organic layer, 30 nm thick, consisting of
Alq host doped with 1.2 vol. % Li;
[0167] (4) a p-type doped organic layer, 60 nm thick, consisting of
NPB host doped with 6 vol. % F.sub.4-TCNQ
[0168] [Li doped Alq(30 nm)/F.sub.4-TCNQ doped NPB(60 nm) consists
of the 1.sup.st connecting unit];
[0169] (5) a HTL, 30 nm thick, consisting of NPB;
[0170] (6) a LEL, 30 nm thick, consisting of Alq;
[0171] (7) an ETL 30 nm thick, consisting of Alq host doped with
1.2 vol. % Li;
[0172] [NPB(30 nm)/Alq(30 nm)/Alq:Li(30 nm), denoted as EL2,
consists of the 2.sup.nd EL unit;
[0173] (8) a cathode, approximately 210 nm thick, consisting of
Mg:Ag.
[0174] After the deposition of these layers, the device was
transferred from the deposition chamber into a dry box for
encapsulation. The completed device structure is denoted as
ITO/CFx/EL1/Alq:Li(30 nm)/NPB:F4-TCNQ(60 nm)/EL2/Mg:Ag.
[0175] This cascaded OLED requires a driving voltage of 14.3 V to
pass 20 mA/cm.sup.2. Its luminance is 1166 cd/m.sup.2 and its
luminance efficiency is about 5.8 cd/A, which are twice as high as
those of Example 1. The luminance decay vs. operational time is
shown in both FIGS. 3 and 5. After 300 hours' operation, the
luminance is dropped by about 15%. The voltage evolution vs.
operational time is shown in both FIGS. 4 and 6. It is obvious that
the driving voltage is operationally unstable. After 300 hours'
operation, the driving voltage is increased by 50%.
Example 3 (Inventive)
[0176] A cascaded OLED was fabricated as the same as Example 2
except that NPB was replaced with compound (VI).
[0177] The cascaded device structure is denoted as
ITO/CFx/EL1/Alq:Li(30 nm)/(compound VI):F.sub.4-TCNQ(60
nm)/EL2/Mg:Ag.
[0178] This cascaded OLED requires a driving voltage of 13.5 V to
pass 20 mA/cm.sup.2. Its luminance is 1611 cd/m.sup.2 and its
luminance efficiency is about 8.1 cd/A. The efficiency is higher
while the voltage is lower when compared to Example 2. The
luminance decay vs. operational time is shown in FIG. 3. After 300
hours' operation, the luminance dropped by about 10%. The voltage
evolution vs. operational time is shown is FIG. 4. The voltage
increased by only 1.3%
Example 4 (Inventive)
[0179] A cascaded OLED was fabricated as the same as Example 2
except that NPB was replaced with compound (VII).
[0180] The cascaded device structure is denoted as
ITO/CFx/EL1/Alq:Li(30 nm)/(compound VII):F.sub.4-TCNQ(60
nm)/EL2/Mg:Ag.
[0181] This cascaded OLED requires a driving voltage of 13.2 V to
pass 20 m/cm.sup.2. Its luminance is 1619 cd/m.sup.2 and its
luminance efficiency is about 8.1 cd/A. The efficiency is higher
and the voltage is lower when compared to Example 2. The luminance
decay vs. operational time is shown in FIG. 3. After 300 hours'
operation, the luminance dropped by about 12%. The voltage
evolution vs. operational time is shown in FIG. 4. There was no
voltage increase.
Example 5 (Inventive)
[0182] A cascaded OLED was fabricated as the same as Example 2
except that NPB was replaced with compound (X).
[0183] The cascaded device structure is denoted as
ITO/CFx/EL1/Alq:Li(30 nm)/(compound X):F.sub.4-TCNQ(60
nm)/EL2/Mg:Ag.
[0184] This cascaded OLED requires a driving voltage of 15.3 V to
pass 20 mA/cm.sup.2. Its luminance is 1580 cd/m.sup.2 and its
luminance efficiency is about 7.9 cd/A. The efficiency is higher
and the voltage is slightly higher when compared to Example 2. The
luminance decay vs. operational time is shown in FIG. 3. After 300
hours' operation, the luminance dropped by about 15%. The voltage
evolution vs. operational time is shown in FIG. 4. There was no
voltage increase.
Example 6 (Inventive)
[0185] A cascaded OLED was fabricated as the same as Example 2
except that NPB was replaced with compound (XIII).
[0186] The cascaded device structure is denoted as
ITO/CFx/EL1/Alq:Li(30 nm)/(compound XIII):F.sub.4-TCNQ(60
nm)/EL2/Mg:Ag.
[0187] This cascaded OLED requires a driving voltage of 12.5 V to
pass 20 mA/cm.sup.2. Its luminance is 1466 cd/m.sup.2 and its
luminance efficiency is about 7.3 cd/A. The efficiency is higher
and the voltage is slightly less when compared to Example 2. The
luminance decay vs. operational time is shown in FIG. 5. After 300
hours' operation, the luminance dropped by about 14%. The voltage
evolution vs. operational time is shown in FIG. 6. There is a
voltage increase of about 23%.
Example 7 (Inventive)
[0188] A cascaded OLED was fabricated as the same as Example 2
except that NPB was replaced with compound (XIV).
[0189] The cascaded device structure is denoted as
ITO/CFx/EL1/Alq:Li(30 nm)/(compound XIV):F.sub.4-TCNQ(60
nm)/EL2/Mg:Ag.
[0190] This cascaded OLED requires a driving voltage of 15.8 V to
pass 20 mA/cm.sup.2. Its luminance is 1598 cd/m.sup.2 and its
luminance efficiency is about 8.0 cd/A. The efficiency is higher
and the voltage is a bit higher when compared to Example 2. The
luminance decay vs. operational time is shown in FIG. 5. After 300
hours' operation, the luminance dropped by about 20%. The voltage
evolution vs. operational time is shown in FIG. 6. There is a
voltage increase of about 2.8%.
Example 8 (Inventive)
[0191] A cascaded OLED was fabricated as the same as Example 2
except that NPB was replaced with compound (XV).
[0192] The cascaded device structure is denoted as
ITO/CFx/EL1/Alq:Li(30 nm)/(compound XV):F.sub.4-TCNQ(60
nm)/EL2/Mg:Ag.
[0193] This cascaded OLED requires a driving voltage of 12.7 V to
pass 20 mA/cm.sup.2. Its luminance is 1427 cd/m.sup.2 and its
luminance efficiency is about 7.1 cd/A. The efficiency is higher
and the voltage is slightly when compared to Example 2. The
luminance decay vs. operational time is shown in FIG. 5. After 300
hours' operation, the luminance dropped by about 14%. The voltage
evolution vs. operational time is shown in FIG. 6. There is a
voltage increase of about 6.9%.
Example 9 (Inventive)
[0194] A cascaded OLED was fabricated as the same as Example 2
except that NPB was replaced with compound (XIV) and a 4-nm-thick
Sb.sub.2O.sub.5 layer was disposed between the Li doped Alq layer
and the F.sub.4-TCNQ doped compound (XIV) layer in the connecting
unit.
[0195] The cascaded device structure is denoted as
ITO/CFx/EL1/Alq:Li(30 nm)/Sb.sub.2O.sub.5(4 nm)/(compound
XIV):F.sub.4-TCNQ(60 nm)/EL2/Mg:Ag.
[0196] This cascaded OLED requires a driving voltage of 15.5 V to
pass 20 mA/cm.sup.2. Its luminance is 1589 cd/m.sup.2 and its
luminance efficiency is about 8.0 cd/A. When compared to Example 7,
the efficiency is about the same and the voltage is slightly lower.
The luminance decay vs. operational time is shown in FIG. 7. After
300 hours' operation, the luminance dropped by about 12%. The
voltage evolution vs. operational time is shown in FIG. 8. There is
no voltage increase during the 300 hours operation of the
device.
[0197] The above examples demonstrate that a significant increase
in luminance efficiency can be achieved by using a cascaded OLED
structure containing the new p-type host materials of the present
invention compared to the cascaded OLED using NPB as p-type host.
Additionally, the voltage is considerably more stable for the new
p-type hosts versus that of NPB. As is shown by Example 9, the
voltage can be stabilized even further if we insert an interfacial
layer.
[0198] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
Parts List
[0199] 100 cascaded OLED
[0200] 110 anode
[0201] 120 EL unit
[0202] 120.1 1.sup.st EL unit
[0203] 120.2 2.sup.nd EL unit
[0204] 120. 3.sup.rd EL unit
[0205] 120.(N-1) (N-1).sup.th EL unit
[0206] 120.N N.sup.th EL unit
[0207] 130 connecting unit
[0208] 130.1 1.sup.st connecting unit
[0209] 130.2 2.sup.nd connecting unit
[0210] 130.(N-1) (N-1).sup.th connecting unit
[0211] 131n-type doped organic layer
[0212] 132 interfacial layer
[0213] 133 p-type doped organic layer
[0214] 140 cathode
[0215] 150 voltage/current source
[0216] 160 electrical conductors
* * * * *